What's the rarest/most expensive retro game you own?

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I got Daze Before Christmas on Megadrive in the box which is worth $1200 AUD, picked it up for like $10 from cash converters 30 years ago and play it every Christmas as a tradition.

Next is Conker's Bad Fur Day which goes for $350 AUD now apparently.

Who knows, maybe oneday I'll need the money lmao

Anyone else own any rare or valuable stuff?